The invention relates generally to anemometers and more specifically concerns an anemometer that utilizes a radionuclide counting technique for measuring both the direction and velocity of wind.
There are several types of anemometers currently in use for both applied research and industrial applications. Many types of anemometers are designed to furnish only a single component of wind velocity; cup anemometers are an example. However, some physical situations warrant knowledge of the three components of wind velocity. Appropriate anemometers have been designed to furnish this information. A discussion of the advantages and the limitations of various types of anemometers can be found in Kaimal, J.C., Sensors and Techniques for Direct Measurement of Turbulent Fluxes and Profiles in the Atmospheric Surface Layer., Atmos. Technol., No. 7, Fall 1975, pp. 7-14. The characteristics of some of them are briefly summarized below.
The hot wire and hot film type anemometers, which depend on the cooling power of the wind, are in general of small size and well suited for use in a wide range of atmospheric pressures. For transient flow measurements, the hot wire anemometer has no rival. Its frequency response extends to several hundred kHz. However, calibration is found to change with ambient temperature, with contamination of the wire, and with prolonged use. The hot wire instruments are fragile and not very suitable for large wind direction fluctuations. The hot film instruments, on the other hand, are more rugged and also offer the advantage of substantial signal-to-noise ratio gain due to the high resistance of the film, though their frequency response extends only to a few kHz. The main use of the hot film anemometers has been the measurement of turbulent liquids, though they can be used for the measurement of turbulent fluctuations in gases as well.
The three-axis sonic anemometer is based on the fact that the speed of sound increases or decreases depending on whether the sound is traveling in the direction of the wind or against the wind. This anemometer simultaneously measures the three components of velocity and seems to be sensitive only to wind components along the acoustic paths. Its frequency response is limited only by path length, and its calibration remains stable for extended periods. However, path averaging limits use of this type of anemometer to heights of 4 meters and above.
In the case of anemoclinometers, which are small in size, the wind velocity components are determined from pressure differences between the various sets of points on a metal sphere. The frequency response is reasonably good, limited only by the time constant of pressure transducers, but the probe needs to be oriented into the wind.
Remote wind velocity measurements in the atmosphere using laser doppler methods have also been reported. These methods are nonintrusive, have advantages of remote sensing in inacessible locations, and provide good velocity resolution. However, they require powerful lasers and rather delicate signal processing equipment.
Finally, the three axis propeller anemometers and the propellers-on-bivane anemometers are simple in design and moderate in cost. However, these anemometers are hampered by the limitations on their response, inherent in their structures.
It is the primary object of this invention to provide an anemometer utilizing a radionuclide counting technique that measures both velocity and direction of wind.
Another object of the invention is provide an anemometer that could be portable and yet not too fragile.
A further object of the invention is to provide a small economical anemometer that requires low power.
Still another object of this invention is to provide an anemometer that can be used for extended periods of time even in remote inhospitable places which are not easily accessible.
Other objects and advantages of this invention will become apparent hereinafter.